llvm/lib/Target/AArch64/AArch64PBQPRegAlloc.cpp

   1 //===-- AArch64PBQPRegAlloc.cpp - AArch64 specific PBQP constraints -------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 // This file contains the AArch64 / Cortex-A57 specific register allocation
   9 // constraints for use by the PBQP register allocator.
  10 //
  11 // It is essentially a transcription of what is contained in
  12 // AArch64A57FPLoadBalancing, which tries to use a balanced
  13 // mix of odd and even D-registers when performing a critical sequence of
  14 // independent, non-quadword FP/ASIMD floating-point multiply-accumulates.
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "AArch64PBQPRegAlloc.h"
  18 #include "AArch64.h"
  19 #include "AArch64RegisterInfo.h"
  20 #include "llvm/CodeGen/LiveIntervals.h"
  21 #include "llvm/CodeGen/MachineBasicBlock.h"
  22 #include "llvm/CodeGen/MachineFunction.h"
  23 #include "llvm/CodeGen/MachineRegisterInfo.h"
  24 #include "llvm/CodeGen/RegAllocPBQP.h"
  25 #include "llvm/Support/Debug.h"
  26 #include "llvm/Support/ErrorHandling.h"
  27 #include "llvm/Support/raw_ostream.h"
  28
  29 #define DEBUG_TYPE "aarch64-pbqp"
  30
  31 using namespace llvm;
  32
  33 namespace {
  34
  35 #ifndef NDEBUG
  36 bool isFPReg(unsigned reg) {
  37   return AArch64::FPR32RegClass.contains(reg) ||
  38          AArch64::FPR64RegClass.contains(reg) ||
  39          AArch64::FPR128RegClass.contains(reg);
  40 }
  41 #endif
  42
  43 bool isOdd(unsigned reg) {
  44   switch (reg) {
  45   default:
  46     llvm_unreachable("Register is not from the expected class !");
  47   case AArch64::S1:
  48   case AArch64::S3:
  49   case AArch64::S5:
  50   case AArch64::S7:
  51   case AArch64::S9:
  52   case AArch64::S11:
  53   case AArch64::S13:
  54   case AArch64::S15:
  55   case AArch64::S17:
  56   case AArch64::S19:
  57   case AArch64::S21:
  58   case AArch64::S23:
  59   case AArch64::S25:
  60   case AArch64::S27:
  61   case AArch64::S29:
  62   case AArch64::S31:
  63   case AArch64::D1:
  64   case AArch64::D3:
  65   case AArch64::D5:
  66   case AArch64::D7:
  67   case AArch64::D9:
  68   case AArch64::D11:
  69   case AArch64::D13:
  70   case AArch64::D15:
  71   case AArch64::D17:
  72   case AArch64::D19:
  73   case AArch64::D21:
  74   case AArch64::D23:
  75   case AArch64::D25:
  76   case AArch64::D27:
  77   case AArch64::D29:
  78   case AArch64::D31:
  79   case AArch64::Q1:
  80   case AArch64::Q3:
  81   case AArch64::Q5:
  82   case AArch64::Q7:
  83   case AArch64::Q9:
  84   case AArch64::Q11:
  85   case AArch64::Q13:
  86   case AArch64::Q15:
  87   case AArch64::Q17:
  88   case AArch64::Q19:
  89   case AArch64::Q21:
  90   case AArch64::Q23:
  91   case AArch64::Q25:
  92   case AArch64::Q27:
  93   case AArch64::Q29:
  94   case AArch64::Q31:
  95     return true;
  96   case AArch64::S0:
  97   case AArch64::S2:
  98   case AArch64::S4:
  99   case AArch64::S6:
 100   case AArch64::S8:
 101   case AArch64::S10:
 102   case AArch64::S12:
 103   case AArch64::S14:
 104   case AArch64::S16:
 105   case AArch64::S18:
 106   case AArch64::S20:
 107   case AArch64::S22:
 108   case AArch64::S24:
 109   case AArch64::S26:
 110   case AArch64::S28:
 111   case AArch64::S30:
 112   case AArch64::D0:
 113   case AArch64::D2:
 114   case AArch64::D4:
 115   case AArch64::D6:
 116   case AArch64::D8:
 117   case AArch64::D10:
 118   case AArch64::D12:
 119   case AArch64::D14:
 120   case AArch64::D16:
 121   case AArch64::D18:
 122   case AArch64::D20:
 123   case AArch64::D22:
 124   case AArch64::D24:
 125   case AArch64::D26:
 126   case AArch64::D28:
 127   case AArch64::D30:
 128   case AArch64::Q0:
 129   case AArch64::Q2:
 130   case AArch64::Q4:
 131   case AArch64::Q6:
 132   case AArch64::Q8:
 133   case AArch64::Q10:
 134   case AArch64::Q12:
 135   case AArch64::Q14:
 136   case AArch64::Q16:
 137   case AArch64::Q18:
 138   case AArch64::Q20:
 139   case AArch64::Q22:
 140   case AArch64::Q24:
 141   case AArch64::Q26:
 142   case AArch64::Q28:
 143   case AArch64::Q30:
 144     return false;
 145
 146   }
 147 }
 148
 149 bool haveSameParity(unsigned reg1, unsigned reg2) {
 150   assert(isFPReg(reg1) && "Expecting an FP register for reg1");
 151   assert(isFPReg(reg2) && "Expecting an FP register for reg2");
 152
 153   return isOdd(reg1) == isOdd(reg2);
 154 }
 155
 156 }
 157
 158 bool A57ChainingConstraint::addIntraChainConstraint(PBQPRAGraph &G, unsigned Rd,
 159                                                  unsigned Ra) {
 160   if (Rd == Ra)
 161     return false;
 162
 163   LiveIntervals &LIs = G.getMetadata().LIS;
 164
 165   if (Register::isPhysicalRegister(Rd) || Register::isPhysicalRegister(Ra)) {
 166     LLVM_DEBUG(dbgs() << "Rd is a physical reg:"
 167                       << Register::isPhysicalRegister(Rd) << '\n');
 168     LLVM_DEBUG(dbgs() << "Ra is a physical reg:"
 169                       << Register::isPhysicalRegister(Ra) << '\n');
 170     return false;
 171   }
 172
 173   PBQPRAGraph::NodeId node1 = G.getMetadata().getNodeIdForVReg(Rd);
 174   PBQPRAGraph::NodeId node2 = G.getMetadata().getNodeIdForVReg(Ra);
 175
 176   const PBQPRAGraph::NodeMetadata::AllowedRegVector *vRdAllowed =
 177     &G.getNodeMetadata(node1).getAllowedRegs();
 178   const PBQPRAGraph::NodeMetadata::AllowedRegVector *vRaAllowed =
 179     &G.getNodeMetadata(node2).getAllowedRegs();
 180
 181   PBQPRAGraph::EdgeId edge = G.findEdge(node1, node2);
 182
 183   // The edge does not exist. Create one with the appropriate interference
 184   // costs.
 185   if (edge == G.invalidEdgeId()) {
 186     const LiveInterval &ld = LIs.getInterval(Rd);
 187     const LiveInterval &la = LIs.getInterval(Ra);
 188     bool livesOverlap = ld.overlaps(la);
 189
 190     PBQPRAGraph::RawMatrix costs(vRdAllowed->size() + 1,
 191                                  vRaAllowed->size() + 1, 0);
 192     for (unsigned i = 0, ie = vRdAllowed->size(); i != ie; ++i) {
 193       unsigned pRd = (*vRdAllowed)[i];
 194       for (unsigned j = 0, je = vRaAllowed->size(); j != je; ++j) {
 195         unsigned pRa = (*vRaAllowed)[j];
 196         if (livesOverlap && TRI->regsOverlap(pRd, pRa))
 197           costs[i + 1][j + 1] = std::numeric_limits<PBQP::PBQPNum>::infinity();
 198         else
 199           costs[i + 1][j + 1] = haveSameParity(pRd, pRa) ? 0.0 : 1.0;
 200       }
 201     }
 202     G.addEdge(node1, node2, std::move(costs));
 203     return true;
 204   }
 205
 206   if (G.getEdgeNode1Id(edge) == node2) {
 207     std::swap(node1, node2);
 208     std::swap(vRdAllowed, vRaAllowed);
 209   }
 210
 211   // Enforce minCost(sameParity(RaClass)) > maxCost(otherParity(RdClass))
 212   PBQPRAGraph::RawMatrix costs(G.getEdgeCosts(edge));
 213   for (unsigned i = 0, ie = vRdAllowed->size(); i != ie; ++i) {
 214     unsigned pRd = (*vRdAllowed)[i];
 215
 216     // Get the maximum cost (excluding unallocatable reg) for same parity
 217     // registers
 218     PBQP::PBQPNum sameParityMax = std::numeric_limits<PBQP::PBQPNum>::min();
 219     for (unsigned j = 0, je = vRaAllowed->size(); j != je; ++j) {
 220       unsigned pRa = (*vRaAllowed)[j];
 221       if (haveSameParity(pRd, pRa))
 222         if (costs[i + 1][j + 1] !=
 223                 std::numeric_limits<PBQP::PBQPNum>::infinity() &&
 224             costs[i + 1][j + 1] > sameParityMax)
 225           sameParityMax = costs[i + 1][j + 1];
 226     }
 227
 228     // Ensure all registers with a different parity have a higher cost
 229     // than sameParityMax
 230     for (unsigned j = 0, je = vRaAllowed->size(); j != je; ++j) {
 231       unsigned pRa = (*vRaAllowed)[j];
 232       if (!haveSameParity(pRd, pRa))
 233         if (sameParityMax > costs[i + 1][j + 1])
 234           costs[i + 1][j + 1] = sameParityMax + 1.0;
 235     }
 236   }
 237   G.updateEdgeCosts(edge, std::move(costs));
 238
 239   return true;
 240 }
 241
 242 void A57ChainingConstraint::addInterChainConstraint(PBQPRAGraph &G, unsigned Rd,
 243                                                  unsigned Ra) {
 244   LiveIntervals &LIs = G.getMetadata().LIS;
 245
 246   // Do some Chain management
 247   if (Chains.count(Ra)) {
 248     if (Rd != Ra) {
 249       LLVM_DEBUG(dbgs() << "Moving acc chain from " << printReg(Ra, TRI)
 250                         << " to " << printReg(Rd, TRI) << '\n';);
 251       Chains.remove(Ra);
 252       Chains.insert(Rd);
 253     }
 254   } else {
 255     LLVM_DEBUG(dbgs() << "Creating new acc chain for " << printReg(Rd, TRI)
 256                       << '\n';);
 257     Chains.insert(Rd);
 258   }
 259
 260   PBQPRAGraph::NodeId node1 = G.getMetadata().getNodeIdForVReg(Rd);
 261
 262   const LiveInterval &ld = LIs.getInterval(Rd);
 263   for (auto r : Chains) {
 264     // Skip self
 265     if (r == Rd)
 266       continue;
 267
 268     const LiveInterval &lr = LIs.getInterval(r);
 269     if (ld.overlaps(lr)) {
 270       const PBQPRAGraph::NodeMetadata::AllowedRegVector *vRdAllowed =
 271         &G.getNodeMetadata(node1).getAllowedRegs();
 272
 273       PBQPRAGraph::NodeId node2 = G.getMetadata().getNodeIdForVReg(r);
 274       const PBQPRAGraph::NodeMetadata::AllowedRegVector *vRrAllowed =
 275         &G.getNodeMetadata(node2).getAllowedRegs();
 276
 277       PBQPRAGraph::EdgeId edge = G.findEdge(node1, node2);
 278       assert(edge != G.invalidEdgeId() &&
 279              "PBQP error ! The edge should exist !");
 280
 281       LLVM_DEBUG(dbgs() << "Refining constraint !\n";);
 282
 283       if (G.getEdgeNode1Id(edge) == node2) {
 284         std::swap(node1, node2);
 285         std::swap(vRdAllowed, vRrAllowed);
 286       }
 287
 288       // Enforce that cost is higher with all other Chains of the same parity
 289       PBQP::Matrix costs(G.getEdgeCosts(edge));
 290       for (unsigned i = 0, ie = vRdAllowed->size(); i != ie; ++i) {
 291         unsigned pRd = (*vRdAllowed)[i];
 292
 293         // Get the maximum cost (excluding unallocatable reg) for all other
 294         // parity registers
 295         PBQP::PBQPNum sameParityMax = std::numeric_limits<PBQP::PBQPNum>::min();
 296         for (unsigned j = 0, je = vRrAllowed->size(); j != je; ++j) {
 297           unsigned pRa = (*vRrAllowed)[j];
 298           if (!haveSameParity(pRd, pRa))
 299             if (costs[i + 1][j + 1] !=
 300                     std::numeric_limits<PBQP::PBQPNum>::infinity() &&
 301                 costs[i + 1][j + 1] > sameParityMax)
 302               sameParityMax = costs[i + 1][j + 1];
 303         }
 304
 305         // Ensure all registers with same parity have a higher cost
 306         // than sameParityMax
 307         for (unsigned j = 0, je = vRrAllowed->size(); j != je; ++j) {
 308           unsigned pRa = (*vRrAllowed)[j];
 309           if (haveSameParity(pRd, pRa))
 310             if (sameParityMax > costs[i + 1][j + 1])
 311               costs[i + 1][j + 1] = sameParityMax + 1.0;
 312         }
 313       }
 314       G.updateEdgeCosts(edge, std::move(costs));
 315     }
 316   }
 317 }
 318
 319 static bool regJustKilledBefore(const LiveIntervals &LIs, unsigned reg,
 320                                 const MachineInstr &MI) {
 321   const LiveInterval &LI = LIs.getInterval(reg);
 322   SlotIndex SI = LIs.getInstructionIndex(MI);
 323   return LI.expiredAt(SI);
 324 }
 325
 326 void A57ChainingConstraint::apply(PBQPRAGraph &G) {
 327   const MachineFunction &MF = G.getMetadata().MF;
 328   LiveIntervals &LIs = G.getMetadata().LIS;
 329
 330   TRI = MF.getSubtarget().getRegisterInfo();
 331   LLVM_DEBUG(MF.dump());
 332
 333   for (const auto &MBB: MF) {
 334     Chains.clear(); // FIXME: really needed ? Could not work at MF level ?
 335
 336     for (const auto &MI: MBB) {
 337
 338       // Forget Chains which have expired
 339       for (auto r : Chains) {
 340         SmallVector<unsigned, 8> toDel;
 341         if(regJustKilledBefore(LIs, r, MI)) {
 342           LLVM_DEBUG(dbgs() << "Killing chain " << printReg(r, TRI) << " at ";
 343                      MI.print(dbgs()););
 344           toDel.push_back(r);
 345         }
 346
 347         while (!toDel.empty()) {
 348           Chains.remove(toDel.back());
 349           toDel.pop_back();
 350         }
 351       }
 352
 353       switch (MI.getOpcode()) {
 354       case AArch64::FMSUBSrrr:
 355       case AArch64::FMADDSrrr:
 356       case AArch64::FNMSUBSrrr:
 357       case AArch64::FNMADDSrrr:
 358       case AArch64::FMSUBDrrr:
 359       case AArch64::FMADDDrrr:
 360       case AArch64::FNMSUBDrrr:
 361       case AArch64::FNMADDDrrr: {
 362         Register Rd = MI.getOperand(0).getReg();
 363         Register Ra = MI.getOperand(3).getReg();
 364
 365         if (addIntraChainConstraint(G, Rd, Ra))
 366           addInterChainConstraint(G, Rd, Ra);
 367         break;
 368       }
 369
 370       case AArch64::FMLAv2f32:
 371       case AArch64::FMLSv2f32: {
 372         Register Rd = MI.getOperand(0).getReg();
 373         addInterChainConstraint(G, Rd, Rd);
 374         break;
 375       }
 376
 377       default:
 378         break;
 379       }
 380     }
 381   }
 382 }